Toilet flange extender

Gents,
A new tile floor has resulted in a finished surface 3/4 of an inch above the existing 4" cast iron flange which is seated in the concrete slab floor. The inside of the cast iron pipe - where it is level with the flange - is slightly irregular (lead?) and may make it difficult to insert a rubber gasket in to the 4" pipe. I plan on installing a new low flow toilet and would appreciate advice on selecting an extender and gasket.

Besure to seal between the flange and extender(s), and secure the extenders because plastic has a tendency to "warp" over time if it is not firmly anchored.

Click to expand...

Yes, and that's in the instructions for the Sioux Chief extenders as well (printed on the ring.) Don't let the big box store former "plumbers" talk you out of this sealing step by telling you, "I never do that."